Race condition on new language calling getNodeAtLocation

[AndreasArvidsson]

The tree map is dependent on the events onDidChangeVisibleTextEditors and onDidChangeTextDocument to add new languages when needed.

Quickly changing language on a file or switching to a file with a different language and immediately calling getNodeAtLocation throws an exception "Can't read property rootNode of undefined".

One solution would be that in getNodeAtLocation do the following:

• Check if a tree exists for the current document.
  • If true return result
• If false check if language is supported
  • If false throw a proper exception Language {lang} is not supported by the tree parser
• if true update the tree
• Return result

Similar thoughts might be applied to the function getTree

[pokey]

This approach seems reasonable, the only slight annoyance being that getNodeAtLocation would have to become async, because it might need to load the wasm, which is async. This async-ness then becomes contagious, so eg in cursorless, transformSelection becomes async as well, and then everything up the chain from there 😕. Not sure I see a better alternative tho. Any ideas?

[AndreasArvidsson]

I have no better solution. If you really want to keep it synchronous I guess you could always do a busy wait via a loop.

[pokey]

In #5, I opted to just raise a special exception (LanguageStillLoadingError) for this case. Client code can catch the exception and try again. If desired, I could add a separate version of the function that is async, but I think I'd prefer to keep the default implementation sync and just throw an exception